The present invention relates to the field of tertiary butyl alcohol production, and more particularly to the production of high purity tertiary butyl alcohol.
There is a commercial demand in the United States for various grades of tertiary butyl alcohol ("TBA"). Tertiary butyl alcohol with relatively high concentrations of impurities is acceptable for use as a denaturant for ethyl alcohol. Many billions of pounds of tertiary butyl alcohol are also used in gasoline blends. Tertiary butyl alcohol produced for this purpose has a typical purity of about 96%, with major impurities being isopropyl alcohol ("IPA"), isobutyl formate ("IBF"), acetone, water, methyl ethyl ketone ("MEK") and tertiary-butyl formate ("TBF"). High purity tertiary butyl alcohol is also in demand for use as a pharmaceutical and specialty solvent, and for use in the manufacture of organic peroxides. Such high purity tertiary butyl alcohol typically contains less than 0.5% impurities. At the present time, Shell Chemical Company supplies nearly the entire domestic market for high purity tertiary butyl alcohol, which is believed to be produced by the hydration of isobutylene.
It would be advantageous to provide a simple, efficient process for purifying lower grades of tertiary butyl alcohol so that they will contain less than 0.5% impurities. Many of the impurities contained in gasoline grade tertiary butyl alcohol can be separated by conventional distillation and it has been found that production run purities ranging between 99.2% and 99.6% can be obtained using such processes. The major impurity in such refined tertiary butyl alcohol is isopropyl alcohol. Since some users of high purity tertiary alcohol demand purities in excess of 99.8%, the provision of a technique for producing tertiary butyl alcohol under production conditions in such purities is in considerable demand.
Since isopropyl alcohol boils at 82.4.degree. C. and tertiary butyl alcohol boils at 82.2.degree.-3.degree. C., conventional distillation is not suitable for separating these compounds. Similarly, purification of tertiary butyl alcohol to 99.8% purity is not feasible by extractive distillation with alkane solvents since it has been found that alkane solvents form a minimum boiling azeotrope with TBA.